1. Field
The present disclosure relates to a filter including a bulk acoustic wave resonator.
2. Description of Related Art
Recently, due to the rapid development of mobile communications devices, chemical and biological devices, and the like, demand for a smaller and lighter filter, oscillator, resonant element, acoustic resonant mass sensor, or the like, used in such devices, has also increased.
As a means of implementing such a small and light filter, oscillator, resonant element, and acoustic resonant mass sensor, a film bulk acoustic resonator (hereinafter, referred to as an “FBAR”) is used. The FBAR may be mass-produced at a minimal cost, and may be implemented to have a subminiature size. In addition, the FBAR may be implemented to have a high-quality factor (Q) value, which is a main characteristic of a filter that may be used even in a microwave frequency band, and other bands of a personal communications system (PCS) and a digital cordless system (DCS).
In general, the FBAR includes a resonant part implemented by sequentially stacking a first electrode, a piezoelectric layer, and a second electrode on a substrate.
An operational principle of the FBAR will be described hereinafter. First, when electrical energy is applied to the first and second electrodes to induce an electric field in a piezoelectric layer, the electric field generates a piezoelectric phenomenon in the piezoelectric layer to allow the resonant part to vibrate in a predetermined direction. Resultantly, a bulk acoustic wave is generated in the same direction as the direction in which the resonant part vibrates, resulting in resonance.